Deep-sea oil releases from accidents during offshore exploratory drilling or production are of particular concern, as the potential for such accidents increases with the expansion of the offshore industry to more extreme environments. During the 2010 Deepwater Horizon, huge amounts of oil were released into the Gulf of Mexico, adversely affecting marine wildlife. What prevented a worse outcome was the ability of nature to biodegrade oil. To this end, the community oi spill model MEDSKIL-II has been modified to incorporate biodegradation kinetics of dissolved oil and oil droplets dispersed in the water column. Biodegradation of oil can be modelled by Monod kinetics or as a first order decay process. The kinetics of oil particles size reduction due to the microbe-mediated degradation at water-oil particle interface is represented by the shrinking core model. Furthermore, a Lagrangian plume module has been developed and coupled to MEDSLIK-II, for predicting the fate of the spill until reaching the sea surface. The Lagrangian plume model is represented by elements that trace the plume’s trajectory. Each Lagrangian element represents a mixture of water, oil and gas. Changes in the mass and composition of the element are accounted for by the turbulent entrainment of ambient water, leakage of gas bubbles and oil droplets from the plume, dissolution of gas in seawater, and formation or disintegration of gas hydrates. The motion of the element is computed from the conservation equations for mass, momentum, and buoyancy. Biodegradation kinetics are also represented in the model, to enhance prediction of fate and transport of deep-sea spills.
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